While windows are a desirable architectural detail in buildings, they typically account for 30% of heating and cooling costs. Double pane windows help reduce heat transfer and were originally achieved by hanging a second (single pane) window over the outside of the existing window; however they couldn't be opened, so this was for winter use and known as a “storm window”. A more convenient alternative is a multi-pane permanent replacement window, but this is much more expensive. For the less expensive storm window approach the difficulty of seasonally installing and removing exterior storm windows was at least partly addressed by converting to double or triple track storms that could be opened and closed from inside the house. Finally, to avoid the cost of multi-track storm windows, insulating window panels have been developed as interior storm windows, which are much easier to seasonally install and remove. These take many forms from permanent to semi-permanent to temporary (e.g., flimsy heat shrinking plastic sheets). Other than the largely unsatisfactory temporary kind, insulating window panels (storm windows) for interior or exterior use are generally either expensive, or bulky and difficult to employ. Also, in most cases a storm window must be custom made to fit in an existing window opening, and therefor either requires a degree of skill to make and install it, or it must be shipped in a full size assembled state, which can be relatively expensive, and then it requires skilled installation, generally using some kind of mechanical fastener that can mar the existing window trim.
Thus there is a need for improved means and methods for insulating existing windows in a cost effective manner. It is an object of the present invention to reduce the cost of window insulation products, while maintaining the convenience and effectiveness of the better forms of prior art storm windows.